No effect of oral or sample temperature on sensory assessment of fat content

Physiology & Behavior, Vol. 56, No. 4, pp. 655-658, 1994 Copyright © 1994 ElsevierScienceLtd Printed in the USA. All rights reserved 0031-9384/94 $6.00 + .00

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No Effect of Oral or Sample Temperature on Sensory Assessment of Fat Content DAVID

J. M E L A , l K E I T H R. L A N G L E Y

AND

ALAN

MARTIN

Consumer Sciences Department, Institute o f Food Research, Earley Gate, Whiteknights Road, Reading RG6 2EF, UK R e c e i v e d 9 D e c e m b e r 1993 MELA, D. J, K. R. LANGLEY AND A. MARTIN. No effect of oral or sample temperature on sensoryassessmentoffat content. PHYSIOL BEHAV 56(4) 655-658, 1994.--This work examined the possible influences of oral and sample temperature on the perception of fat content of a model food system. Melting or related phenomena may contribute to the greater sensation of fat content and the highly acceptable textural characteristics associated with certain fats. Thirty-one adults assessed the fat content of 0%, 12%, 24%, 36%, and 48% oil-in-water emulsions prepared with a commercial cocoa butter substitute having a melting range of 17-41°C. Samples were evaluated at combinations of sample and mouth temperatures of 20 and 36°C, with oral temperatures manipulated by repeated cold- and warm-water rinses prior to assessments. There were no significant differences amongst these treatments on perceived fat content of the samples, nor were subject characteristics of age or body composition related to judgments of fat content in these stimuli. Although previous studies had shown that degree of fat saturation is associated with enhanced perception of fat content (11), that does not appear to be related to the degree or occurrence of melting in the mouth over the ranges studies here. Fat

Perception

Temperature

Melting

Sensory evaluation

A growing body of human and animal research focusses on individual differences in the sensory perception and acceptance of dietary fats, as well as the possible underlying bases for their ingestion (7,8). However, there is limited published information with regard to the basic psychophysics of food lipids. It is clear that humans are capable of gauging the fat content of real and modified fluid dairy products ( 1 - 3 , 9 , 1 3 - 1 5 ) , and such judgments appear to be largely, if not wholly, derived from oral textural cues (9,10). However, most of these studies have utilized complex stimuli such as milk and cream, which differ not only in fat content, but appearance, flavour intensity and profile, viscosity, and the size and number of fat particles. More detailed examinations of the characteristics that impart the textural sensations associated with fat content have only recently been undertaken, focussing on fluid milk products (16,17) and model oilin-water emulsions (11). We have recently shown that a more saturated fat source generates an increased sensation of fat content in a sample, compared to a relatively unsaturated fat at the same fat content (11). This appears to be primarily due to the greater viscosity of the more saturated fat, but could also be partly due to melting. Many food fats that are valued for their textural qualities (e.g., butter oil, cocoa butter, and other tropical oils) are largely comprised of saturated fatty acids, and share the property of relatively rapid melting near oral temperatures, thus undergoing the phase transition from solid to liquid upon ingestion.

Age

Body composition

One way of testing the contribution of melting to the sensation of the presence of fat is to alter the degree and speed of melting in the mouth, and assess the effect on perceived fat content. Previous studies have shown that the perceived intensity of certain tastants in water may be lower at ambient vs. body temperature, an effect that may be predominantly related to cooling of the lingual surface, rather than the stimulus temperature per se (4). Purified fats have no taste, and the perception of fat content probably has little or no direct involvement with the gustatory sensory apparatus. However, variations in oral temperature alone might effect changes in other sensory systems; hence, the present study examined influences of both oral and stimulus temperature on perception of fat content in a liquid emulsion. METHOD

Subjects Eight males and 23 females, with a mean age of 46.3 years (range 18-81), were recruited by public advertisement. Criteria for exclusion included the following: use of tobacco products, restricted or unusual dietary regimens (e.g., weight loss or diabetic diets), food intolerances or other contraindications for ingestion of the test stimuli, and health conditions or use of medications reported to influence sensory perception. The experimental details were approved by the Institute of Food Re-

J To whom requests for reprints should be addressed. 655

656

search Ethics Committee and all subjects signed an inlormed consent document prior to their participation. Previous studies have identified possible associations between body composition and hedonic ratings, though not intensity judgments of fat-containing stimuli (1,11,12,14). To allow investigation of the latter issue, each subject was measured for height and weight, and body composition was determined by bioelectrical impedance analysis (Model BIA-101; R. J. L. Systems, Inc., Detroit, MI) (6). To ensure a stable level of hydration for body composition analyses, participants emptied their bladders just prior to this procedure, and had been asked not to exercise strenuously or consume alcohol for the preceding 24 h. They were also requested to refrain from gum chewing, brushing their teeth, or eating or drinking anything except plain water for at least 2 h before sensory testing. Subjects were naive as to the contents of the samples and the true purpose of the studies.

MELA. LANGLEY AND MARTIN

for a period sufficient to evaluate a sample. These conditions were intended to maximize (cold stimulus, warm mouth) or minimize iwarm stimulus, cold mouth) melting of the Hycoa 5, as well as to allow possible differential effects of oral and stimulus temperature to be distinguished. Samples (10 ml) were presented in 30-ml opaque plastic medicine cups. The series of 20 samples was presented once to each subject, with the order of samples randomized within blocks of all fat levels at a single mouth temperature. Orders of mouth temperatures were also randomized. Subjects were requested to place the entire 10-ml sample in their mouth, evaluate it for 3 5 s, expectorate, and then score the sample for "fat content" on a nine-point category scale ranging from "absent" to "'extreme" (9). The temperature manipulation procedures served as a rinse between samples.

Statistical Analyses Stimuli Oil-in-water emulsions were prepared with 0%, 12%, 24%, 36%, and 48% w/w Hycoa 5, a highly saturated commercial cocoa butter substitute formulated from hydrogenated palm kernel oil (Loders Croklaan Ltd., London) in deionized water, with sucrose stearate (product #S1570, Mitsubishi-Kasei Food Corporation, Tokyo, Japan) present at 1% w/w as an emulsifier. This sugar ester is suitable for a wide range of oil phase volumes and has little discernible taste or aroma. Hycoa 5 has a melting range of 17-41°C, and is 80% and 7% solid at 20 and 36°C, respectively. Samples were prepared by slowly stirring water at 50-60°C into a weighed quantity of emulsifier to form a paste, which was then further diluted with the balance of the water. Hycoa 5 was injected into this mixture at 10 ml min -~, adjacent to the operating head of a Silverson homogenizer (Vortmix, Hampton, Middlesex, UK) The mixture was then recycled past the homogenizer head of a reverse-flow microfluidizer (Model M- 120E, Christianson Scientific Equipment Ltd., Gateshead, UK) operating at 300 bar pressure, for a total residual time of 4 min, and stored at 4°C for up to 48 h before use. Mean particle sizes of approximately 0.3-0.4 #m have previously been reported (11 ), and no substantial degree of agglomeration of fat particles has been found under these storage conditions. Stimulus viscosities were determined at shear rates between 12 and 270 s-~, on a Brookfield (Loughton, Essex, UK) LVT cone and plate viscometer at 20.0 and 36 + 0.2°C. These emulsions show non-Newtonian, shear-thinning behaviour, with the viscosity decreasing as a power function of increases in shear rate. The interpolated viscosity at 48 s -~ was used, as previous research has indicated that this shear rate may be most analogous to human oral assessment of liquids (19).

Repeated-measures analysis of variance (ANOVA) was used to assess the overall main and interactive effects of fat levels and oral and stimulus temperatures on sensory judgments, using SPSS/PC + statistical software (Version 3.1, SPSS Inc., Chicago, IL). Some of the responses from one subject were lost, so analyses were carried out on the remaining 30 subjects. A probability of p <- 0.05 was used as the criterion for statistical significance. Because of possible relationships between adiposity and perception of fats, and the wide range of ages, subjects were classified by median splits into high and low groups for age (median = 41 years) and for percent body fat (median values 21% and 31% body fat for males and females, repectively), and these groupings were entered as between-subjects factors in post hoc analyses. Median splits for classification by body fat used sexspecific values, because males normally have a much lower body fat content than females. RESULTS

Instrumental measures of viscosity showed fat-containing emulsions were more viscous at 20°C than at 36°C (Fig. 1). However, these differences did not appear to be reflected in sensory responses. Although Fig. 2 shows the clear effects of fat level on perceived fat content, F(4, 116) = 164.6, p < 0.001, no other main effects or interactions approached statistical significance (all p > 0.20), except that sensory ratings tended to be marginally higher in the cool mouth conditions, F(1, 29) = 3.18, p = 0.085. There were no significant main or interactive effects related to subject characteristics of age and body composition, although

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Protocol All testing was carried out in single sessions of approximately 60-min duration, in purpose-built individual sensory testing booths. Visual differences between samples were masked by low-intensity red light, and possible influences of differences in odour release from the stimuli were eliminated by the use of nose clips throughout the evaluations. During testing, sets of stimuli were kept at 36 and 20°C in constant-temperature water baths. Oral temperatures were manipulated using rinse procedures similar to those of Green and Frankmann (4). For the 20 and 36°C mouth conditions, subjects rinsed five times with iced or 40°C water, respectively. Pretesting with temperature probes indicated that this reduced mouth temperature to the target temperatures

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FIG. 1. Viscositiesof Hycoa 5 oil-in-wateremulsions at 20 and 36°C.

TEMPERATURE AND ASSESSMENT OF FAT CONTENT

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FIG. 2. Perceived fat content of oil-in-water emulsions vs. actual fat content, at combinations of stimulus and oral temperatures of 20 and 36°(=. Standard errors at each point range from 0.20-0.34. within-subject variation was somewhat greater in the older age group, F(14, 14) = 2.45, p = 0.05. There were also no main or interactive effects related to sex; however, the number of male subjects (n = 8) was relatively small. DISCUSSION Oral and solution temperature, and related melting phenomena, were not found to influence the gauging of fat content in these model stimuli. Using similar sensory methods, we have previously shown that fat saturation and fat particle size in a lowviscosity oil can significantly influence such sensory ratings, primarily through effects on viscosity (11). However, in the present study, colder, more viscous samples were not judged higher in fat content than warm samples of similar fat content. Differences in viscosity of this magnitude have been shown to effect differences in perceptions of fat content of similar stimuli tested under similar conditions (11). Unfortunately, there is a paucity of existing literature and hypotheses that might be used to guide interpretation of these results. To a large extent, most work relating emulsion particle and textural characteristics has been proprietary in nature. It is possible that learned contextual factors may influence this normally predominant effect of viscosity. Specifically, there may be a degree of involuntary compensation for the greater viscosity of colder samples, related to casual familiarity and experience with this phenomenon in everyday life. Many liquid and semisolid food emulsions (e.g., liquid and whipped cream, custard, salad dressing) become discemably less viscous as they rise from refrigerated to ambient temperatures. An analogous situation may

657

also hold for perception of such stimuli at different oral temperatures. A second possibility is that the emulsifier coat on fat particles in such stimuli either restrict phase transitions and other changes in the structure of internal triglyceride core (5) or limit the extent to which such physical changes may be sensed. Excess emulsifier free in solution may also make some contribution to the sensation of fat content. These possibilities could be tested by carrying out similar experiments with media containing unemulsified fats. As noted, though, stimulus temperature was clearly associated with differences in sample viscosity, to a degree that should have been sufficient to elicit changes in sensory ratings. However, our previous work indicates that other characteristics of fats, beyond viscosity, may make significant independent contributions to sensations of fat content (9,11). Temperature changes may not affect these characteristics in the same way that viscosity is changed. The precise extent of melting that might occur under the experimental extremes used here cannot be readily determined. Our calculations suggest that the energy imparted or absorbed by the mouth under the respective cold sample/warm mouth and warm sample/cold mouth conditions would be insufficient to melt or harden all of the fat in the samples, especially at the higher fat levels. Such a complete phase change would require considerably longer periods of holding the sample in the mouth, during which oral as well as sample temperature would change substantially. Analyses of the effects of age and body composition revealed no effects of either independent measure. In a previous study, we found no consistent differences between older and younger adults in their gauging of fat content of these types of emulsions (11). However, others have suggested that elderly subjects may have reduced ability to detect the textural sensations of emulsified fats (18,20). Schiffman et al. (18) reported that elderly subjects (mean age 87.3 years) had significantly elevated thresholds for emulsified oils relative to young subjects (mean age 23.7 years). In the present study, the difference in ages was not so extreme, with the younger and older groups averaging 32.7 and 59.1 years of age, respectively. However, subsequent analyses based on the youngest and oldest 10 subjects (mean 30.2 and 67.0 years, respectively) also indicated no age-related effects. The issue of fat and texture perception in aging remains open for more directed investigation. The present results are clearly in agreement with previous studies, which indicate no differences between lean and obese subjects with regard to perception of fat content in liquid stimuli (1,11,14). This study indicates quite clearly that under conditions associated with differences in fat solidification and viscosity, there were no significant effects of oral or solution temperature on perceived fat content of oil-in-water emulsions. Along with previous studies (9,11), these results support an important role for unspecified stimulus factors beyond viscosity as important determinants of the sensation of fat content.

REFERENCES 1. Drewnowski,A.; Brunzell, J. D.; Sande, K.; Iverius, P. H.; Greenwood, M. R. C. Sweet tooth reconsidered: Taste responsiveness in human obesity. Physiol. Behav. 35:617-622; 1985. 2. Drewnowski, A.; Greenwood, M. R. C. Cream and sugar: Human preferences for high-fat foods. Physiol. Behav. 30:629-633; 1983. 3. Giovanni, M. E.; Pangbom, R. M. Measurement of taste intensity and degree of liking of beverages by graphic scales and magnitude estimation. J. Food Sci. 48:1175-1182; 1983. 4. Green, B. G.; Frankmann, S. P. The effect of cooling the tongue on the perceived intensity of taste. Chem. Senses 12:609-619; 1987.

5. Javanaud, C.; Gladwell, N. R.; Gouldby, S. J.; Hibberd, D. J.; Thomas, A.; Robbins, M. M. Experimentaland theoretical values of the ultrasonic properties of dispersions: Effect of particle state and size distributions.Ultrasonics 29:331-337; 1991. 6. Lukaski, H. C.; Johnson, P. E.; Bolonchuk, W. W.; Lykken, G. 1. Assessmentof fat-free mass using bioelectricalimpedancemeasurements of the human body. Am. J. Clin. Nutr. 41:810-817; 1985. 7. Mela, D. J., Cal.Dietary fats: Determinantsof preference, acceptance, and consumption. London: Elsevier Applied Science; 1992. 8. Mela,D. J. The perceptionand acceptanceof dietary fat: What, who, why? Br. Nutr. Fdn. Nutr. Bull. 17(Suppl 1):74-86; 1992.

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9. Mela, D. J. Sensory assessment of fat content in fluid dairy products. Appetite 10:37-44; 1988. 10. Mela, D. J.; Christensen, C. M. Sensory assessment of oiliness in a low moisture food. J. Sensory Stud. 2:273-281; 1988. 1 I. Mela, D. J.; Langley, K.: Martin, A. Sensory assessment of fat content: Effect of emulsion and subject characteristics. Appetite 22:67 81; 1994. 12. Mela, D. J.; Sacchetti, D. S. Sensory preferences for fats in foods: Relationships to diet and body composition. Am. J. Clin. Nutr. 53:908-915; 1991. 13. Monneuse, M.-O.; Bellisle, F.; Louis-Sylvestre, J. Impact of sex and age on sensory evaluation of sugar and fat in dairy products. Physiol. Behav. 50:1111-1117; 1991. 14. Pangborn, R. M.; Bos, K. E. O.; Stem, J. S. Dietary fat intake and taste responses to fat in milk by under-, normal, and overweight women. Appetite 6:25-40; 1985. 15. Pangborn, R. M.; Giovanni, M. A. Dietary intake of sweet foods and

MELA, LANGLEY

16. 17.

18.

19.

20.

AND MARTIN

of dairy l~tts and resultant gustatory responses to sugar in lemonade and to fat in milk. Appetite 5:317--327: 1984. Richardson, N. J. The perception of cream texture. PhD dissertation, University of Birmingham, Birmingham. UK; 1992. Richardson, N. J.; Booth, D. A.; Stanley, N. L. Effect of homogenization and fat content on oral perception of low and high viscosity model creams. J. Sensory Stud. 8:133-143; 1993. Schiffman, S. S.; Graham, B. G.; Vance, A. R.; Gaillard, K.; Warwick, Z. S.; Erickson, R. P. Detection thresholds for emulsified oils in young and elderly subjects. Chem. Senses 17:693; 1992 ¢abstract). Sharma, F.; Sherman, P. Identification of stimuli controlling the sensory evaluation of viscosity I1. Oral methods. J. Texture Stud. 4:111-118; 1973. Warwick, Z. S,; Schiffman, S. S. Sensory evaluations of fat-sucrose and fat-salt mixtures: Relationship to age and weight status. Physiol. Behav. 48:633-636: 1990.